This invention relates to therapeutic radiation oncology and to an improved method of manufacture of radioactive seed implants.
Radioactive pellets or "seeds" have been used to treat cancerous tumors, especially in the prostate gland, for many years. These seeds usually are about 4 mm long and 0.8 mm in diameter and emit low energy x-rays in the 20-40 keV range. The first such source utilized Iodine-125 (.sup.125 I) with a 60-day half life. More recently, Palladium-103 (.sup.103 Pd) with a 17-day half life has been used.
U.S. Pat. No. 3,351,049 to Lawrence discloses a method of impregnating a carrier body with a radioactive liquid containing Iodine-125, Palladium-103, Cesium-131, Xenon-133, or Ytterbium-169. After drying, the carrier body is then encapsulated in a welded canister, e.g., of titanium. Kubiatowitz in U.S. Pat. No. 4,323,055 discloses a method of coating radioactive Iodine-125 on to the surface of specially prepared X-ray detectable rods, e.g., silver rods. These coated silver rods are then encapsulated within a canister, e.g., of titanium, to create a sealed source.
Another method, disclosed by Carden in U.S. Pat. No. 5,405,309 uses cyclotron produced palladium-103 which is electroplated onto one or more pellets of electroconductive material, e.g., graphite rods, and subsequently encapsulated in a shell, such as a welded titanium canister.
Another method disclosed by Coniglione in U.S. Pat. No. 5,713,828 employs a double-walled tubular structure which is hollow along its major axis. This type of construction is stated to reduce the migration of seeds by affording better attachment to tissue. The hollow, double-walled tube also permits a rod of suture material to be placed through the seed for better linear placement of seeds during the clinical procedure.
Coniglione also discloses a non-radioactive pre-seed in which a precursor isotope is plated or otherwise coated onto a substrate prior to neutron activation. This technique cannot produce iodine-125 seeds where the precursor isotope is xenon-124, which, being an inert gas, cannot be plated or otherwise coated onto a substrate. In addition, for a palladium-103 seed the method of Coniglione in fabricating a non-radioactive pre-seed generally requires use of isotopically pure palladium-102 precursor that is electroplated onto a substrate. Natural palladium cannot be used because the presence of palladium-106 would produce a long-lived contaminant radiation which would be unacceptable to the radiation oncologist because it would expose the patient to unwanted gamma radiation. Such high purity enriched palladium-102 must be purchased from, for example, Oak Ridge National Laboratories or other commercial suppliers at high cost. Palladium-102 enriched to 78 atomic percent is available from Oak Ridge at a price of about $868,000 per gram.
In addition, these enriched isotopes cannot be electroplated on non-conductor substrates such as silicon or plastics. Coniglione teaches that these non-conductive substrates must first be metallized prior to plating with the enriched isotope.
All of the above mentioned technologies have the disadvantage that one must work with highly radioactive liquids which takes a high level of skill and is relatively expensive, or use a physical coating or electroplating technique to form the radioactive precursor or radioactive layer on a carrier body.